AbstractDilband iron ore
deposits, discovered in 1997 by Geological Survey of Pakistan (GSP)
in Kalat Division Balochistan, Pakistan, is of significant
importance from socio-economical point of view among the rest
indigenous iron ore deposits discovered so far in Pakistan. Because
of its relatively low iron content, high gangue minerals specially
quartz and more importantly high phosphorous ( i.e. steel polutant)
content, it requires an adequate concentration method, in order to
meet the requirements of Pakistan Steel Mills ore specification (i.e.
57-60% Fe (min.), 8.5% SiO2 (max.), 0.5% Al2O3 (max.), 0.1% P
(max.), and 0.05% S. This work, therefore, is aimed to up-grade
Dilband iron ore through an adequate physical concentration methods.
This calls for detailed mineralogical, petrological, elemental, and
intergrown investigations as these studies are widely recognized to
be the mandatory steps in the selection of an appropriate
concentration method and play significant role in developing the
cost effective process flow sheets.
For mineralogical, petrographic, and elemental analysis XRD, thin
section and SEM attached with EDS, and Atomic Absorption
Spectrometer and XRF techniques were used. Mineralogical study
revealed that Dilband iron ore is mainly composed of 46.27%
hematite, 17.41% quartz 14.47% calcite, 9.24% chlinochlore, 10.5%
kaolinite, and 1.75% fluorapatite minerals. Three types of iron
stones namely hematite-ooides, hematite-peloids, and hematite
biosparite were identified from petrographic study. Elemental
analysis of different size fractions ranging from 600 Ám down to 38
Ám indicated that Dilband iron ore contains average of 40.18% Fe,
18.34% SiO2, 5.32% Ca, and 2.262% Al. Whereas, average analysis of
different size fractions on XRF indicated 44.3% Fe, 20.4% SiO2, 8.8%
CaO, 6.35% Al2O3, 1.3% P2O5, and 0.065% SO2. From the mineralogical,
X-ray mapping with EDS, and elemental analysis data finely
dissemination of impurities specially quartz, and fluorapatite in
hematite phase was conceived, suggesting that Dilband iron ore is
not amenable to upgrade with conventional physical techniques.
For assessing the mesh of liberation the physico-chemical attributes
of different size fractions along with the examination of coarser to
ultra fine particles under reflected microscope, polarized
microscope, stereomicroscope and scanning electron microscope
attached with EDS at different accelerating voltages and
magnifications was conducted. The results of density, magnetic
susceptibility, and elemental analysis revealed that mesh of
liberation of Dilband iron ore exists below 15 Ám particle size. The
image analysis of particles and x-ray mapping results confirmed that
gangue minerals are so finely disseminated that complete liberation
of hematite phase is seldom to achieve even below 10 Ám.
Particularly quartz (SiO2) phase is so finely disseminated within
the matrix of hematite that even in the particles of 2 to 5 Ám the
100% hematite phase was not observed. Interlocking of quartz and
calcite within the 80% hematite enriched particles was observed in
the most of the particles finer than 15 Ám. Acid treatment tests of
the ore using hydrofluoric acid and hydrochloric acid further
confirmed that exact mesh of liberation exist below 2Ám.
Based on these studies selective flocculation process was envisaged
to be the adequate process for beneficiation of Dilband iron ore.
For this, determination of energy required for comminuting to
probable mesh of liberation, zetapotential measurement, content of
polyvalent metal ions, slurry stablization and finally the selective
flocculation was performed. Besides this ore enrichment by means of
density and magnetic separation prior to subsequent selective
flocculation tests were also attempted.
Work index of two size classes of Dilband iron ore was calculated
from grindability tests. Based on grindability test results the work
index value calculated for 3800Ám 80% passing was 11.85 kwh/t and
that for 5200Ám 80% passing was 9.3 kwh/ton. Ball mill grinding test
indicated that dry grinding in open circuit is not efficient and
consumes energy of 88.48kwh/t of ore for grinding 1000/40Ám to 80%
<40Ám size. In dispersion tests effect of particle size, solid
concentration, pH, dispersants and their doses, stirring speed, and
sonication, has been extensively studied. The point of zero charge (PZC)
of Dilband iron ore system was determined by using the Zetaphormeter
III (CAD E400), and found at 4.25 in acid range. The dispersion
results confirmed the significant role of particle size in the
slurry stabilization and the optimal conditions for <38 Ám Dilband
iron ore slurry were found at 10% solid concentration, 10.5 pH ,
2000 rpm stirring speed and 5min stirring time. The optimization of
dispersant and its dose found quite difficult due to marginal change
in sediment wt% , however on the basis of elemental analysis and
sediment wt% 6.4k g/ton (i.e. 400% of stacheometric amount of Ca+2
cation present in Dilband iron ore) of EDTA was recommended.
Selective flocculation tests of Dilband iron ore slurry using corn
starch, potato starch and polyacrylamide (PAA) flocculants were
conducted. The selective flocculation results carried out on Dilbnad
iron ore suggest that either the selective flocculation process is
not the adequate beneficiating technique to upgrade the ore upto the
requirements of the Pakistan SteelMills or it achieves nearly half
of the beneficiation results expected. Applying flotation to
selectively flocculated ore do not upgrade it further due to high
intergrowth status of impurities.
Pre enrichment attempts were also made to check magnetic
susceptibility attribute. It was found to give some better results
in separating less intergrwon from highly intergrwon particles of
-500 and +315Ám size fraction. Results indicated that 60% removal of
P2O5 and 30% of SiO2 is possible with density followed by magnetic
separation. Substential decrease in silica and phosphorous content
in less intergronwn part suggest that a process flow sheet based on
magnetic susceptibility attribute would be a suitable route to some
exent for Dilband iron ore.